TORONTO — It’s considered one of the greatest roles that an actress can play, a tragic heroine cut from the same transcendent cloth as Hedda Gabler and Madame Bovary. Keira Knightley calls Anna Karenina “one of the fascinations.” And now, at age 27, the actress can check that fascination off her “to do” list.

After breaking through as a teenager hot for soccer (“Bend It Like Beckham”), Knightley has played, among other things, a swashbuckler (the “Pirates of the Caribbean” franchise), a bounty hunter (“Domino”), a gambling-addicted socialite (“The Duchess”), an organ-donor clone (“Never Let Me Go”), and a trailblazing psychoanalyst (“A Dangerous Method”). With the opening of “Anna Karenina” on Friday, the London native notches her third collaboration with fellow Brit Joe Wright, who previously directed her in “Pride & Prejudice” and “Atonement.” If lavish costume dramas were awards bait, Knightley and Wright would be nomination magnets. Oh, wait, they are.

Focus Features

Knightley and director Joe Wright on the set of “Pride & Prejudice.”

When we sat down with Knightley at the recent Toronto International Film Festival, where “Anna Karenina” screened to mixed reviews (“beautiful but unmoving” wrote the UK’s Daily Mail), the actress was engaging, salty, and much softer looking than you might expect from her famously bony onscreen image. She had plenty to say about taking on the title heroine of Leo Tolstoy’s epic 19th-century novel, a married aristocrat who is spurned by Russian high society when she has an affair with a dashing young count. And she wasn’t shy about making real-life contemporary connections to the cold, judgmental behavior in this classic.

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She admitted that “Anna,” rewarding as it was, took so much out of her that she’s spent the last several months acting in less weighty fare — the upcoming “Can a Song Save Your Life?” with Mark Ruffalo, and Kenneth Branagh’s “Jack Ryan” franchise reboot.

A. Did [Garbo] play it twice? Two different versions? Did one of them really not work?

Q. One of them was silent.

A. Oh, I’ve not seen that. Well, she really liked that character then, didn’t she?

Q. What would make you want to step into such a daunting role?

A. I think any character is daunting, but it wasn’t as terrifying as Elizabeth Bennet in “Pride & Prejudice,” because women see themselves as Elizabeth Bennet. They fall in love with her, they want to be her. With Anna Karenina, they don’t want to end up like her and they don’t really fall in love with her. They are fascinated by her, which means that there is a lot of room for interpretation within the portrayal of her.

Q. Were you always fascinated by her?

A. I remember reading the book when I was in my late teens, early 20s, and I just remember it as this sort of sweeping, beautiful love story, and her being innocent, wonderful. And then I read it last summer, just before we started, and I went, “Oh, this is something very other than I remember it. This is something much darker, and she is much darker than I remember her.” … There were certain moments when I was reading it when I went “Tolstoy hates her.”

Q. How do you take all that Anna is in that massive novel and a) make her work onscreen, and b) make her your own?

A. The thing that I was really conscious of was just not to simplify her. In quite a few versions, she has been played as a victim, she has been played as the innocent, and that’s not how I see her.

Q. Were you trying to make her more relatable?

A. It wasn’t a matter of really trying. You do judge her, and then you suddenly go “Am I any better than her?” And the answer is no. That’s mostly the case when we judge people, and we as a society do — that’s how we solidify ourselves, that’s what the pack mentality is, we turn against the individual and judge them in order to make ourselves feel better.

JoJo Whilden/Miramax Films

Q. Do you think about the melodrama in these big roles? How much is too much?

A. Well, you never want to hit the same pitch twice. If you went to 10 every single time it would just get boring — for you doing it and for the people watching it.

Q. Have you and Joe Wright been plotting to do this movie for a while?

A. We did start talking about it when I did “Atonement” — I think I was 21. It was not along the lines of “We should do this right now” but along the lines of “Who are the great female characters?” Anna came up and Hedda Gabler came up and Antigone came up. I had just read [“Anna Karenina”], so I was going “Oh my God, it would be amazing.”

Q. Are you going to knock off those others one by one?

A. I should, shouldn’t I? I should just tick those off [laughs]. Um, yeah, this did seem like the right time to do Anna. I mean, when [Wright] phoned up and said “Do you fancy it?,” it was instant. Though I probably would have said yes when I was younger as well, because how can you say no?

Q. Tell me about your working relationship with Joe.

A. [Feigns exasperation] I don’t know. People keep saying “Why does this work?” I [expletive] wish I knew why this works; it would make it so much easier. He’s somebody who demands 150 percent from everybody. That’s why I love working with him — because it’s nothing less than everything. And when you’re making something so frivolous as a film, it should actually mean everything.

Q. I read somewhere that you said “I don’t find perfect faces very interesting.” Does that sound like you?

Alex Bailey/Focus Features

A. Possibly. You never really see perfect faces, do you? Is there a perfect face? I think imperfections are always the interesting bit. And I find that in characters. My mum always said “Blessed imperfections.” And she’s quite right. All art, all drama, it’s all about the imperfections within people. I suppose that does go to the aesthetic as well. I don’t believe that anything can be perfect. And it should not be perfect.

Q. But as an actress you’re subject to a lot of scrutiny, particularly where it comes to your weight. What’s it like living in that constant spotlight? It’s a career you elected, but still . . .

A. Absolutely. It is a visual medium so you can’t expect that the visual side of it isn’t paramount. I mean, yes, it’s very difficult. But there is immense pressure to look a certain way and that’s not just for an actress. It is a difficult thing for any young woman to navigate. You see a picture of me and I’m too skinny, or you see a picture of me in a bikini and I’ve got cellulite, and both of those are bad things. This idea of anybody that could possibly be perfect is, again, ridiculous.

Q. Speaking of scrutiny, your role in “A Dangerous Method” was polarizing for a lot of people — some thought you overplayed it and some thought you hit it just right. What do you make of that?

A. That was always going to be one that did that. It was that even when [director] David Cronenberg went, “That’s what I want.” I think it was partly, yes, subverting this face [she cups her chin], but equally just a fascinating character. And working with David, who does go to extremes, I figured I might as well go to the extreme. I have a very subtle taste; I never like to go too far. To break out of the rigidity of my taste and to create this strange being who is very definitely other and polarizing, that was incredibly freeing and very exciting.

Q. Is it also good, and necessary, for developing a tough skin?

A. I think I’ve always had that because people always said I was [expletive]. The idea of doing something that was intentionally polarizing was actually quite liberating.

Q. Do you take any of your roles home with you at night? Do they affect you offscreen?

A. Anna did. Definitely. I think because of the intense nature of the way that we were doing it. As much as she is this complex character and incredibly emotional being, trying to balance that with the technical side of trying to create something so stylized did mean that she was a constant presence. And I probably wasn’t the easiest person to live with.

Q. Did the people in your life say they couldn’t wait for filming to end?